It is known in the internal engine combustion art to provide means for insulating engine exhaust port walls to retard the loss of heat from the engine exhaust gases. One purpose, among others, of such constructions is to retain heat in the engine exhaust gases to improve the performance of connected emission control equipment, such as catalytic converters or thermal reactors.
Among arrangements which have been proposed for reducing heat loss through the engine exhaust port walls is the provision of suitable liners in the exhaust ports. Various constructions have been proposed including sheet metal liner inserts and liners of various hardened ceramic materials. It is desirable that such liners be resistant to corrosion and abrasion from the exhaust gases which pass therethrough and that they be of adequate strength and light weight (low mass) to provide extended life without adding excessively to the overall weight of the engine. The insulating characteristics of the liner are, of course, also important.